Helically wound flexible hoses are commonly used to convey fluids. These hoses must be flexible enough to allow nobility during use, yet durable enough to withstand the normal abuses associated with their environment, such as being dragged upon a surface such as a floor, being stepped upon, etc. These flexible hoses can be subjected to both pressure and vacuum and must be able to sustain both of these forces.
Flexible hoses are often used to convey liquid chemicals. In liquid chemical applications, the hose must be able to withstand the pressure or vacuum of the application, the environment, and additionally must be chemically resistant. Prior art hoses built for chemical applications are formed of a flexible material, or web, and a more rigid material that are helically wound in an interlocking manner to form a tubular channel. The more rigid material has a circular or oval cross-section and typically, a portion of the cross-section extends radially outwardly beyond the flexible material on the exterior surface of the hose. This radially outwardly extending portion of the cross-section of the more rigid material helps to prevent damage to the flexible material, such as that caused by friction from the hose being dragged across a surface.
Problems with the prior art hoses arose when customers began demanding hoses having a greater chemical resistance and an ability to withstand higher pressures. Some materials that provide excellent chemical resistance have low strengths and, in the prior art configuration are unable to withstand the pressures demanded by the customers. Additionally, these hoses are susceptible to failure if the surface of the flexible material becomes damaged because the more rigid material, with a circular or oval cross-section, concentrates the stress or strain caused from bending the hose on the exterior surface of the flexible material. Consequently, when the prior art hose is subject to bending stresses and the high pressure application, the flexible material may peel away from the more rigid material and cause the hose to fail.
U.S. Pat. No. 3,885,594 discloses a reinforced flexible pipe having a tubular wall formed of a soft synthetic material and a reinforcing spiral core of a hard synthetic resin material. The reinforced spiral core is substantially I-shaped and is partly exposed out of the pipe wall.
U.S. Pat. No. 4,120,628 discloses an apparatus for extruding a plastic tube having a spiral or helical tape or filament forming a reinforced skeleton of the tube. The spiral or helical tape or filament has a substantially S-shaped or a round cross-section.
U.S. Pat. No. 4,587,145 discloses a flexible hose comprising soft and hard members alternately disposed in a spiral form. The hose further has a connector element disposed through the center of the thickness of the soft member. The connector element comprises projected portions that are interconnected to the hard member. The connector element further comprises a string member on which projected portions are sewed.